System and method for managing available uplink transmit power

ABSTRACT

A system and method of determining the maximum uplink transmit power of a subscriber station from a remote base station where the subscriber station reports incidents of foldback in its radio to the base station. When the base station receives the report, it reduces the maximum uplink transmit power of the subscriber station. After a period of time lapses without any reports of foldback occurring, the base station increases the maximum uplink transmit power of the subscriber station.

FIELD OF THE INVENTION

The present invention relates to the field of power control in wirelesssystems. More specifically, the present invention relates to determiningat a base station estimates of the available uplink transmit power foreach subscriber station communicating with that base station.

BACKGROUND OF THE INVENTION

In wireless networks, comprising at least one base station and aplurality of subscriber stations, where the network is subject to the“near-far” problem and/or the like, the base station is preferablyinvolved with the management of the transmission power levels of eachsubscriber station. In general, permitting a subscriber station totransmit with more power allows that subscriber station to achieve ahigher data rate, but can also interfere with the transmissions of othersubscriber stations. The tradeoffs between overall network efficiencyversus performance of a particular subscriber station need to becarefully managed.

In addition to network limits, each subscriber station is limited in itsown maximum uplink transmit power by regulatory and/or hardware limits.If a subscriber station transmits at an uplink transmit power levelhigher than its rated uplink transmit power, non-linear effects in thetransmitter's power amplifier can produce errors in the channel.Additionally, for health and safety reasons and for regulatory reasonsto minimize adjacent channel interference, wireless devices arerestricted in the amount of power that they can transmit with, and thisamount is typically less than the maximum possible output of thesubscriber station's power amplifier. For example, a fixed wirelesstransmitter operating at 1.9 MHz may be restricted, by regulation, to amaximum uplink transmit power of 30 dBm. As known to those of skill inthe art, specialized circuitry in the subscriber station's poweramplifier, typically referred to as “foldback circuitry”, is oftenemployed to limit outputted power and prevent the subscriber stationfrom transmitting over-specification and/or outside of regulatorylimits.

When the base station is responsible for admitting subscriber stationsto a higher data rates, the base station needs to know how muchavailable uplink transmit power (i.e., the difference between themaximum uplink transmit power and the current average uplink transmitpower) is available for each subscriber station. The base station doesnot want to assign a data rate to the subscriber station that thesubscriber station is unable to achieve due to an insufficient amount ofavailable uplink transmit power. The base station can make an estimateof available uplink transmit power for a subscriber station by receivingreports of the current uplink transmit power uplink transmit power fromthat subscriber station. However, this estimate may not be accurate dueto variations in the subscriber station's measurement due to operatingtemperatures in the circuitry, a lack of, or limited, calibration ofcircuitry in the subscriber station. Due to these inaccuracies, the basestation may perceive that a subscriber station has more available uplinktransmit power than is actually the case. As such, the base station mayattempt to admit the subscriber station to a higher uplink data rate,requiring a higher uplink transmit power than the subscriber station canactually support, resulting in channel errors and a waste of networkcapacity.

To prevent this problem from occurring, it is typical to provide anuplink transmit power margin to the estimate of available uplinktransmit power to account for variances in each subscriber station.However, providing too large an uplink transmit power margin results ina potentially lower maximum data rate for the subscriber station, whileproviding too small an uplink transmit power margin can result incommunication link errors and a waste of network capacity. As such, itis desired to provide a system and method to determine more accuratelythe amount of available uplink transmit power available to a subscriberstation in order to assign data rates to that subscriber station.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel system andmethod for managing uplink transmit power that obviates or mitigates atleast some of the above-identified disadvantages of the prior art.

According to a first aspect of the present invention, there is provideda method of determining at a base station an estimate of the maximumavailable uplink transmit power of a subscriber station having a radioincluding foldback circuitry and maintaining that estimate at the basestation, the method comprising:

transmitting a message from the subscriber station to the base stationwhenever an incident of foldback occurs at the subscriber station;

decreasing the maintained estimate of the maximum uplink transmit powerof the subscriber station at the base station when the base stationreceives the message from the subscriber station; and

increasing the maintained estimate at the base station when a predefinedperiod of time has lapsed after the base station received the message.

According to another aspect of the present invention, there is provideda system for transmitting data comprising:

a plurality of subscriber stations each operable to transmit a messageindicating an incident of foldback in the subscriber station; and

a base station operable to maintain an estimate of the maximum availableuplink transmit power for each the subscriber station and to receive anythe messages from the plurality of subscriber stations and to reduce themaintained estimate for each the subscriber station which has sent anythe message.

According to another aspect of the present invention, there is provideda system for transmitting data comprising:

at least one subscriber station operable to transmit data at a pluralityof different data rates, the subscriber station further operable totransmit a message indicating an incident of foldback in the subscriberstation; and

a base station operable, upon receiving the message, to reduce the datarate for the subscriber station.

The present invention provides a system and method of determining andmaintaining at a base station an estimate of the maximum availableuplink transmit power of a subscriber station, where the subscriberstation reports incidents of foldback in its radio to the base station.When the base station receives the report, it reduces the estimate ofthe maximum available uplink transmit power of the subscriber station toprevent channel errors. Typically, the base station will also reduce thedata rate for the subscriber station. After a period of time lapseswithout any reports of foldback occurring at the subscriber station, thebase station increases the estimate of the maximum available uplinktransmit power of the subscriber station.

BRIEF DESCRIPTION OF THEY DRAWINGS

A present embodiment of the present invention will now be described, byway of example only, with reference to the attached Figures, wherein:

FIG. 1 is a schematic representation of a wireless network, inaccordance with an embodiment of the invention, comprising a basestation and a plurality of subscriber stations;

FIG. 2 is a representation of a communications link as shown in FIG. 1,comprised of channels having different capacities;

FIG. 3 is a schematic representation of the base station shown in FIG.1;

FIG. 4 is a schematic representation of one of the subscriber stationsshown in FIG. 1;

FIG. 5 is a representation of event messages transmitted betweensubscriber stations and a base station over the communications linkshown in FIG. 2; and

FIG. 6 is a flowchart showing how the base station determines an uplinktransmit power margin for a subscriber station.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a wireless network for transmitting data isindicated generally at 20. Network 20 includes a radio base station 24and a plurality of subscriber stations 28 a, 28 b . . . 28 n. In apresently preferred embodiment, radio base station 24 is connected to atleast one data telecommunications network (not shown), such as a landline-based switched data network, a packet network, etc., by anappropriate gateway and one or more backhauls (not shown), such as a T1,T3, E1, E3, OC3 or other suitable land line link, or a satellite orother radio or microwave channel link or any other link suitable foroperation as a backhaul as will occur to those of skill in the art.

Base station 24 communicates with subscriber stations 28 which, in apresent embodiment of the invention, are installed at subscriberpremises, as is common in a wireless local loop (WLL) system but couldalso be nomadic or mobile stations as will be apparent. The number ‘n’of subscriber stations serviced by a base station 24 can vary dependingupon a variety of factors, including the amount of radio bandwidthavailable and/or the configuration and requirements of the subscriberstations 28.

As illustrated in FIG. 1, the geographic distribution of subscriberstations 28 with respect to base station 24 need not be symmetric norwill subscriber stations 28 which are physically located close to oneanother necessarily experience the same or similar reception qualitiesdue to a variety of factors including the geographic environment (thepresence or absence of buildings which can reflect or mask signals), theradio environment (the presence or absence of radio noise sources), etc.and inherent radio propagation properties, such as Rayleigh fading, etc.Thus, in most circumstances individual subscriber stations 28 served bya base station 24 will have significantly different reception andtransmission qualities from other subscriber stations 28 served by basestation 24 and these qualities will change over time.

As known to those of skill in the art, subscriber stations 28 can begeographically divided into different radio sectors formed via beamforming antennas at base station 24 to increase the number of subscriberstation 28 that can be served from a single base station location. Insuch a case, each sector essentially acts as a different base stationand base station 24 can manage the network resources in each sectorindependent of each other sector. While FIG. 1 shows only one basestation 24 with a single sector, it will further be apparent to those ofskill in the art that network 20 can contain multiple, geographicallydistributed base stations 24, with overlapping sector coverage ofsubscriber stations 28, and where each subscriber station 28 in anoverlapping sector coverage area can select which base station 24, orbase stations, it will be served by.

A communication link 32 is established between base station 24 and eachsubscriber station 28 via radio. Communication link 32 a carriesinformation to be transferred between base station 24 and subscriberstation 28 a, communication link 32 b carries information to betransferred between base station 24 and subscriber stations 28 b, etc.Communication links 32 can be implemented using a variety of multipleaccess techniques, including TDMA, FDMA, CDMA or hybrid systems such asGSM, etc. to obtain links 32 a, 32 b, etc. to respective subscriberstations 28 a, 28 b, etc. In a present embodiment, data transmitted overcommunication link 32 is transmitted using CDMA as a multiple accesstechnology and the data is in the form of packets, encapsulated withinslotted time frames.

As used herein, the terms “package”, “packaged” and “packaging” refer tothe overall arrangement of the transmission of the data for itsreception at an intended destination receiver. Packaging of data caninclude, without limitation, applying different levels of forward errorcorrecting (FEC) codes (from no coding to high levels of coding and/ordifferent coding methods), employing various levels of symbolrepetition, employing different modulation schemes (QPSK, 4-QAM, 16-QAM,64-QAM, etc.) and any other techniques or methods for arranging datatransmission with a selection of the amount of radio (or other physicallayer) resources required for the data rate and the probability oftransmission errors which are appropriate for the transmission. Forexample, data can be packaged with rate 1/4 FEC coding (each 1 data bitis transmitted in 4 bits of information) and 16-QAM modulation fortransmission to a first intended receiver and packaged with rate 1/2 FECcoding and 64-QAM modulation for transmission to a second intendedreceiver, which has a better reception-quality than the first.

Communications link 32 operates in both an uplink (from a subscriberstation 28 to base station 24) and a downlink direction (from basestation 24 to subscriber stations 28). The method of providing bothuplink and downlink direction is not particularly limited, and in thepresent embodiment communications link 32 operates by frequency divisionduplexing (FDD). However, other methods of providing both an uplink anddownlink direction, such as time division duplexing (TDD) and hybridsthereof are within the scope of the invention.

Referring now to FIG. 2, communications link 32 is comprised of aplurality of channels that can be downlink channels, uplink channels orbi-directional channels. In the present CDMA implementation,channelization of the downlink of communications link 32 is achievedwith orthogonal coding of link 32. In the current embodiment, dedicateddata channels (DDCHs) 36 are used as an uplink from subscriber stations28 to base station 24 and are used to carry latency-sensitive traffic inthe downlink from base station 24 to subscriber stations 28. A broadcastdata channel, not shown, can also be employed in the downlink directionto transmit data that is less latency sensitive. DDCHs 36 can beappropriately sized, in both the uplink and downlink directions, toprovide a variety of data rates over varying reception qualitiesexperienced at a subscriber station 28, as needed. For example, DDCH 36a between base station 24 and subscriber station 28 a can be sized toprovide a higher data rate than DDCH 36 b between base station 24 andsubscriber station 28 b.

FIG. 3 shows an example of a base station 24 in greater detail. For thesake of clarity, FIG. 3 shows an example of a single sector base station24. However, as described above, multi-sector base stations 24 are alsowithin the scope of the invention. Base station 24 comprises an antenna40, or antennas, for receiving and transmitting radio-communicationsover communication communications link 32. Antenna 40 is connected to aradio 44 and a modem 48. Modem 48 is connected to amicroprocessor-router assembly 52 such as a Pentium III processor systemmanufactured by INTEL.

Microprocessor-router assembly 52 is responsible for radio resourcemanagement of all subscriber stations 28 within its sector 36. It willbe understood that assembly 52 can include multiple microprocessors, asdesired and/or that the router can be provided as a separate unit, ifdesired. The router within microprocessor-router assembly 52 isconnected to a backhaul 56 in any suitable manner, which in turnconnects base station 24 to a data telecommunications network (notshown).

Referring now to FIG. 4, an example of a subscriber station 28 is shownin greater detail. Subscriber station 28 comprises an antenna 60, orantennas, for receiving and transmitting radio-communications overcommunication communications link 32. Antenna 60 is connected to a radio64 and a modem 68, which in turn is connected to amicroprocessor-assembly 72. Radio 64 includes a power amplifier 76,operable to provide the desired uplink transmit power. Power amplifier76 includes foldback circuitry 80 that monitors a current in poweramplifier 76 indicative of the actual uplink transmit power provided toantenna 60, referred to hereinafter as the “monitored current”. Foldbackcircuitry 80 operates to limit the monitored current to prevent poweramplifier 76 from being driven over specification and/or outsideregulatory limits. When foldback circuitry 80 operates to limit themonitored current, power amplifier 76 is referred to as being in afoldback condition. A foldback condition indicates that subscriberstation 28 is at its maximum uplink transmit power and, as such, has noavailable uplink transmit power.

Microprocessor-assembly 72 can include, for example, a StrongARM orXscale processor manufactured by Intel, that performs a variety offunctions, including implementing A/D-D/A conversion, filters, encoders,decoders, data compressors, de-compressors and/or packetassembly/disassembly. Microprocessor-assembly 72 interconnects modem 68with a data port 84, for connecting subscriber station 28 to a dataclient device (not shown), such as a personal computer, personal digitalassistant or the like which is operable to use data received overcommunication communications link 32. Accordingly,microprocessor-assembly 72 is operable to process data between data port84 and modem 68. Microprocessor-assembly 72 is also interconnected to atleast one telephony port 88, for connecting subscriber station 28 to atelephony device (not shown) such as a telephone or facsimile machine.

A problem with prior art systems is that the base station's estimate ofa subscriber station's available uplink transmit power is ofteninaccurate. As described earlier, temperature variations and a lack ofsufficient calibration in a subscriber station's power amplifier willcause the power amplifier to potentially produce a different uplinktransmit power than what is being reported. If a subscriber station hasless available uplink transmit power than is estimated by the basestation, the base station could instruct that subscriber station to moveto a higher data rate (for example, by changing its modulation schemefrom 32-QAM to 16-QAM) than the subscriber station could currentlyachieve. Foldback circuitry would prevent the subscriber station frombeing overdriven to achieve the desired data rate, resulting intransmission errors. Alternatively, a subscriber station could have moreavailable uplink transmit power than is estimated by the base station.In this situation, the base station will not allow a subscriber stationto achieve its highest possible data rate.

In contrast to the prior art, in the present invention, as part of itsregular operations, each subscriber station 28 tracks incidents offoldback to provide a more accurate estimate to base station 24.Referring now to FIG. 5, each subscriber station 28 maintains a foldbackrecord 100, which is stored on microprocessor-assembly 72. Each timefoldback occurs foldback record 100 is updated. The information storedin foldback record 100 is not particularly limited and can includefoldback information such as the number of consecutive frames in whichfoldback has occurred or the percentage of frames over a period of timein which foldback has occurred or both. Other foldback-relatedinformation that may be usefully stored in foldback record 100 willoccur to those of skill in the art.

Within network 20, the allocation of radio resources is controlled by aradio resource allocation manager (RRAM) 104 which runs onmicroprocessor-assembly 52 of base station 24 or on any otherappropriate computing resource within network 20. RRAM 104 isresponsible for assigning and unassigning DDCHs 36 and for adjustingdata rates in both the uplink and the downlink. The data rate assignedto a DDCH 36 can change over the course of its duration, based on thedemands from subscriber station 28 and the amount of available resourceswithin network 20. RRAM 104 tracks the date rates and other knownoperating values for each subscriber station 28 in a subscriber stationrecord 108. For example, each subscriber station record 108 also storesboth the maximum uplink transmit power (P_(Max)), and the currentaverage uplink transmit power (P_(Ave)) of the subscriber station, asreported by subscriber station 28 to base station 24. Subscriber stationrecord 108 also maintains a uplink transmit power margin (δ_(H)) foreach subscriber station 28 which is used in an attempt to correct forcalibration and temperature-related variations in the maximum uplinktransmit power. The uplink transmit power margin will be described infurther detail below.

As part of its regular operations, subscriber station 28 transmitsdifferent kinds of messages to base station 24. These messages can betransmitted over DDCH 40 or over another channel if a DDCH 40 is notcurrently established between subscriber station 28 and base station 24.

One type of message transmitted periodically from each operatingsubscriber station 28 to base station 24 is a measurement report 112.Measurement reports 112 can include, among other things the receivedsignal strength from base station 24 experienced at a subscriber station28 and the P_(Ave) for the subscriber station 28. Upon receiving ameasurement report 112, RRAM 104 updates the values it has stored forthe subscriber station 28 in a subscriber station record 108.

Another message transmitted from subscriber station 28 to base station24 is a rate increase request 116. In the current embodiment, subscriberstation 28 transmits a rate increase request 116 whenever it has a queueof data to be transmitted which has exceeds a preselected value, or inother words, data to be transmitted is being enqueued at some ratefaster than the data is being transmitted. In response, RRAM 104 willdetermine whether or not it can move subscriber station 28 to a higherdata rate by increasing the size of DDCH 40. RRAM 104 calculates theamount of available uplink transmit power (ΔP_(Available)) for asubscriber station 28. If there is insufficient ΔP_(Available), thenRRAM 104 will not able to increase the size of DDCH 40 and cannot admitsubscriber station 28 to the higher data rate. As will be apparent tothose of skill in the art, available uplink transmit power is only onecriterion in attempting to admit subscriber station 28 to a higheruplink data rate, and other factors are also considered. Other suchfactors can include the management of total sector interference, Qualityof Service (QoS) concerns, and other hardware limitations.

In the current embodiment, RRAM 104 determines available uplink transmitpower using the following formula:ΔP _(Available) =P _(Max) −P _(Ave)

where ΔP_(Available) indicates the amount of available uplink transmitpower for a subscriber station, P_(Max) indicates the maximum uplinktransmit power of subscriber station 28 and P_(Ave) indicates theaverage uplink transmit power, as reported by subscriber station 28 andstored in subscriber station record 104.

As described earlier, the P_(Max) of a subscriber station can varyconsiderably due to a lack of calibration and environmental variations.As such, an uplink transmit power margin (δ_(H)) is applied so thatpower amplifier 76 is not driven out of its intended operating range.RRAM 104 determines the P_(Max) of subscriber station 28 as follows:P _(Max) =P _(SSmax)+δ_(H)

where P_(SSmax) indicates a predetermined maximum uplink transmit powerfor all subscriber stations 28. P_(SSmax) is be the lower of the maximumrated power output of power amplifier 76 and a maximum rated poweroutput set by regulators. In the present embodiment, P_(Ssmax) isdefined as 25 dBm. δ_(H) indicates the current uplink transmit powermargin applied to subscriber station 28. In a present embodiment, δ_(H)can range from a minimum of −3 dBm to a maximum of 6 dBm. Thus asubscriber station 28 with a predetermined P_(SSmax) of 25 dBm havingthe maximum δ_(H) would be considered to have a P_(Max) of 31 dBm forthe purpose of determining ΔP_(Available). How RRAM 104 determines δ_(H)is described in greater detail below.

Another message transmitted from subscriber station 28 to base station24 is a foldback event message 120. As described earlier, subscriberstations 28 track when power amplifier 76 is in a foldback condition.When the foldback value or values stored in foldback record 108 reach apredetermined threshold, a foldback event message 120 reporting anincident of foldback is transmitted to base station 24. Thispredetermined threshold can be adjusted by a network operator to accountfor different local network conditions and for different types offoldback. For example, a foldback event message 120 could be sent whenfoldback record 108 holds a value indicating that 25 or more consecutiveframes have been subject to foldback. Another example would be iffoldback record 108 holds a value indicating that at least 10% of allframes transmitted over a predefined period of time have been subject tofoldback.

Referring now to FIG. 6, a method of determining at base station 24 theuplink transmit power margin (δ_(H)) for a subscriber station 28 isshown beginning at step 200. The method of determining δ_(H) is a methodthat runs continuously within RRAM 104 for each subscriber station 28served by base station 24. At step 200, the method commences with RRAM104 initializing its subscriber station records 104, including the valuefor δ_(H). In the current embodiment, δ_(H) starts at a predeterminedmaximum value, such as 6 dBm, Using the initial value of δ_(H), RRAM 104is able to determine the derived value of P_(Max) using the formuladescribed above. Step 200 occurs upon power-up of base station 24 orwhenever a new subscriber station 28 joins network 20 and is to beserviced by base station 24.

At step 204, RRAM 104 checks to see if it receives a foldback eventmessage 120 from subscriber station 28. If a foldback event messages 120is received, the method advances to step 208. Otherwise the methodadvances to step 212.

At step 208, in response to the receipt of tile foldback event message120, RRAM 104 decreases the uplink transmit power margin (δ_(H)) valuestored for that subscriber station 28. Provided that the value of δ_(H)is greater than the above-mentioned minimum value for δ_(H), the storedvalue of δ_(H) is reduced by a predetermined amount. In the currentembodiment, this predetermined amount is 1 dBm. After reducing the valueof δ_(H), RRAM 104 determines the revised value of P_(Max). The methodthen returns to step 204.

if at step 204, no foldback event message 120 has been received, then atstep 212, RRAM 104 determines whether a predetermined interval haslapsed at subscriber station 28 without any foldback event messages 120being received. In a present embodiment, this predetermined interval is30 minutes, although other predetermined intervals can be employed, asappropriate. If the predetermined interval has lapsed without anyfoldback event messages 120 being received then the method advances tostep 216. Otherwise, the method returns to step 204.

At step 216, if the uplink transmit power margin (δ_(H)) for subscriberstation 28 is less than its maximum value (6 dBm in a presentembodiment), then base station 24 increases δ_(H) for that subscriberstation 28 by a fixed amount (1 dBm in a present embodiment). Afterincreasing the value of δ_(H), RRAM 104 determines the revised value ofP_(Max) Once the uplink transmit power margin δ_(H) has been increased,the method returns to step 204.

While the above method contemplates adjusting δ_(H) by a predeterminedincrement of power, such as 1 dBm, the uplink transmit power margin canbe adjusted in different increments. For example, if foldback eventmessages 120 are transmitted frequently (say, once a minute), then RRAM104 could reduce δ_(H) by a larger increment, e.g. 2 dBm. Conversely, iffoldback event messages 120 are being transmitted relativelyinfrequently (say, once every ten minutes), then RRAM 104 could reduceδ_(H) by a smaller increment, such as 0.5 dBm. Alternatively, subscriberstation 28 can indicate the intensity of the foldback in foldback eventmessage 120. In this case, RRAM 104 could reduce δ_(H) by an amountproportional to the intensity of the foldback condition in subscriberstation 28.

As will undoubtedly be apparent to those of skill in the art, ifsubscriber station 28 transmits a foldback event message 120 to basestation 24, then subscriber station 28 is already transmitting at itsP_(Max). RRAM 104 may determine that subscriber station 28 istransmitting at a higher date than its P_(Max) can reliably support. Assuch, RRAM 104 may instruct subscriber station 28 to move to a lowerdata rate. It is also contemplated that subscriber station 28 could,without receiving instructions from base station 24, reduce its datarate on communications link 32, upon experiencing a foldback condition.For example, if the value in foldback record 100 indicates that least15% of all frames transmitted over a predefined period of time have beensubject to foldback, subscriber station 28 could automatically reduceits data rate on communications link 32. Subscriber station 28 wouldstill send a foldback event message 120 to base station 24 so that basestation 24 would be aware of both the foldback condition in subscriberstation 28 and the changes being made to communications link 32. Othervariations will occur to those of skill in the art.

By receiving foldback event messages 120 from subscriber station 28,RRAM 104 is able to determine a more accurate estimate of the availableuplink transmit power for that subscriber station. Each time a foldbackevent message 120 is received, RRAM 100 decreases δ_(H), which as aresult decreases P_(Max) as well. By decreasing the value of P_(Max),RRAM 100 reduces its estimate of ΔP_(Available) for subscriber station28, ultimately resulting in fewer or no foldback events being reported.After a period of time with no foldback events being reported, RRAM 100increases δ_(H) (thereby increasing the value of P_(Max) and theestimate of ΔP_(Available)). By continuously adjusting δ_(H) both up anddown, RRAM 100 is able to achieve a more reliable estimate ofΔP_(Available). This more reliable estimate of ΔP_(Available) reducesthe number of foldback events experienced by subscriber station 28,(thus reducing the number of link errors caused by subscriber station28) and maximizes the maximum uplink transmit power available tosubscriber station 28.

The above-described embodiments of the invention are intended to beexamples of the present invention and alterations and modifications maybe effected thereto, by those of skill in the art, without departingfrom the scope of the invention which is defined solely by the claimsappended hereto.

1. A method of determining at a base station an estimate of the maximumavailable uplink transmit power of a subscriber station having a radioincluding foldback circuitry and maintaining that estimate at said basestation, said method comprising: transmitting a message from saidsubscriber station to said base station whenever an incident of foldbackoccurs at said subscriber station; decreasing the maintained estimate ofsaid maximum uplink transmit power of said subscriber station at saidbase station when said base station receives said message from saidsubscriber station; and increasing said maintained estimate at said basestation when a predefined period of time has lapsed after said basestation received said message.
 2. The method of claim 1, wherein saidbase station increases said maintained estimate in increments of 1 dBm.3. The method of claim 1, wherein said base station decreases saidmaintained estimate in increments of 1 dBm.
 4. The method of claim 1,wherein said predetermined length of time is 30 minutes.
 5. The methodof claim 1, wherein said incident of foldback includes said radioexperiencing a preselected number of consecutive frames.
 6. The methodof claim 1, wherein said incident of foldback includes said subscriberhaving a foldback duty cycle of more than 10% over a predeterminedperiod of time.
 7. The method of claim 1 wherein said message includesan indication of the degree of foldback imposed at said subscriberstation and said base station decreases said maintained estimateproportionally to the degree of foldback.
 8. A system for transmittingdata comprising: a plurality of subscriber stations each operable totransmit a message indicating an incident of foldback in said subscriberstation; and a base station operable to maintain an estimate of themaximum available uplink transmit power for each said subscriber stationand to receive any said messages from said plurality of subscriberstations and to reduce said maintained estimate for each said subscriberstation which has sent any said message.
 9. The system of claim 8,wherein said base station adjusts the maximum uplink transmit power inincrements of 1 dBm.
 10. The system of claim 8, wherein said basestation increases the maximum uplink transmit power of after apredetermined period of time has lapsed since receiving said messageindicating any incidents of foldback in said radio.
 11. The system ofclaim 10, wherein said predetermined period of time is 30 minutes. 12.The system of claim 8, wherein said incident of foldback includes saidradio experiencing foldback over a preselected number of consecutiveframes.
 13. The system of claim 8, wherein said incident of foldbackincludes said subscriber having a foldback duty cycle of more than apredetermined amount.
 14. The system of claim 8, wherein said basestation adjusts said maximum uplink transmit power of said eachsubscriber station in accordance with the method described in claim 1.15. A system for transmitting data comprising: at least one subscriberstation operable to transmit data at a plurality of different datarates, said at least one subscriber station further operable to transmita message indicating an incident of foldback in said at least onesubscriber station; and a base station operable, upon receiving saidmessage, to reduce the data rate for said at least one subscriberstation.
 16. A subscriber station having a radio including foldbackcircuitry and operable to transmit a message indicating any incidents offoldback in said radio to a base station.
 17. The subscriber station ofclaim 16, wherein an incident of foldback includes said radioexperiencing foldback over a predefined number of consecutive frames.18. The subscriber station of claim 16, wherein said incident offoldback includes said subscriber having a foldback duty cycle of morethan a predetermined amount.
 19. A subscriber station having a radiowith foldback circuitry, said subscriber station operable to transmitdata at a plurality of different data rates, and said subscriber stationfurther operable transmit data at a lower data rate from said pluralityof different data rates after experiencing foldback in said foldbackcircuitry.
 20. A base station operable to receive messages from a remotesubscriber station and further operable to adjust an estimate of themaximum available uplink transmit power maintained for said subscriberstation upon receiving a message indicating an incident of foldback inthe radio of said subscriber station.
 21. The base station of claim 20,wherein said base station adjusts the estimate of maximum availableuplink transmit power in increments of 1 dB.
 22. The base station ofclaim 21, wherein said base station increases the estimate of maximumavailable uplink transmit power of said subscriber station after apredetermined period of time has lapsed since receiving a messageindicating any incidents of foldback in said subscriber station.
 23. Thebase station of claim 22, wherein said predetermined period of time is30 minutes.
 24. The base station of claim 20, wherein said base stationadjusts said maximum available uplink transmit power of said subscriberstation in accordance with the method described in claim
 1. 25. A basestation operable to reduce the data rate of a subscriber station, uponreceiving a message from said subscriber station indicating an incidentof foldback in the radio of said subscriber station.